Resonant circuit



' E. P. 'rl-uAs ,384,504

. RESONANT CIRCUIT Sept. '1 1, 1945;

Filed June ,27, 1944 FIG 2 VENTOR.

I uv EDWIN I e THIAS wwip/aa Arr onnsx Patented Sept. 11, 1945 UNITED STATE 41 a BESONANT cmcurr Edwin r. Hollywood, Calif. Application June 21, 1944, Serial No. 542,422

4 Claims. (01. 250-40) 1 (Granted under the'act of March 3, 1883, as V amended April'30, 1928; 370 O.YG. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

The present invention relates to ultra-highirequency tuning units for wave signal apparatus.

In parallel-resonant tank circuits comprising lumped capacitance and inductance, the common and most expedient method of tuning the tank is by varying its capacitance. The frequency range of the tank circuit lies between the minimum and maximum settings of the variablecapacitor and the limiting factor in the fre. quency range is the valuevof associated induct-.

ance. 1 1

It is frequently desirable in ultra-high-frequency applications to attain a widerv tuning range in a parallel-resonant circuit than can be effected through a complete sweep in the posi-. tion of the shunt variable capacitor and this expansion of range can only be secured through: adjustment of the inductance associated with the circuit. Since the. inductance of an ultra-' high-frequency tank circuit is in the order of microhenries, the use of inductive tuning entailing the use of pigtails or sliding contacts is not feasible. Other prior art arrangements for effecting inductive tuning without slidingcontacts or flexible pigtails involve inductors of relatively large inductance, few. types of which are well adapted for ultra-high-frequency tun- The difiiculties inherent in the prior art methods of wide band tuning of lumped tank circuits at ultra-high-frequencies are in part, obviated in the use of resonant transmission lines having movableshorting bridges as a tumng means. However, this tuning method is mechanically awkward and not adapted to convenient'mampulation from the control panel of a. commercial receiver or transmitter.

Itis, therefore, an object of the present invention to provide a new and improved-wideband ultra-high-irequency tuning unit wherein the eflective inductance of the circuit is varied by capacitative means. a

It is another object of my invention to provide a new and improved ultra-high-frequency tuning unit in which the ratio of inductance to capacitance is maintained throughout the tuning range.

It is a further object of my invention to provide a tuning unit of the above type wherein the components of the circuit are integrally contained in. a unitary assembly.

It is still a further-object of my invention to provide a new and improved ultra-high-fre- I quency tuning unithaving light weight, ruggedness,'and rigidity and one readily adapted to be manuiacturedz with close tolerances in large quantities at lowecost. 1

In accordance withv my present invention, I provide atank circuit'comprising an inductive bra ch ingshunt relation with' a capacitative branch,-the,combination forming a parallelresonant circuit. The inductive branch is com- P sed of "a fixed inductor connectedv in series with a variable capacitor. The values of inductance, and capacitance in the inductive branch are such that within the prescribed operatingirequency range of said branch, the capacitative reactance of any position of the var-.

iable capacitor never exceeds the inductive reactance of the fixed inductor so that the overall impedance is inductiveand in effect the branch acts as a variable inductance- The capacitative branch consists of a variable capacitor which is mechanically ganged to the variable capacitor of the inductive branch and. electrically shunted across said branch. As is well known, the resonantfrequencyof a tankgcircuit is a function ofits inductance and capacitance and is that frequency at which the reactance of the inductive branchis equal and opposed to that of the .capacitative branch. Inasmuch as both branches, inductive and capacitative, undergo concurrent variation by means of. the ganged capacitors; the I'requencyrange encompassed by theabove circuit is far broader than obtainable with conventional resonant circuits.

Moreover, since in certain applications it is desirable to maintain a specific ratio of inductance tocapacitance it-is of importance in wide .band tuning not to substantially upset this ratio.

ln a'power oscillator, for examplerwhere stability is sacrificed for eiflciency, the optimum LC ratio one in which the C is relatively low. Iiin tuning to adesired frequency the capacity oi eztankcircuitis varied whereas the inductanc 'isi'fix'ed'thetank circuit shifts-between a C and'low C ratio, and the efiiciency of the oscillator is thereby affected. In the present invention because of the simultaneous adjustment of the efiective inductance and capacitance of the tank circuit, not only is the resonant frequency changed in large increments during adjustment but the LC ratio is not substantially altered in the process.

effect act as a transmission line while the'capacitors complete the resonant circuit.

For a better understanding of the presentinventicn, together with other and further objects thereof, reference is had to the ensuing detailed description in connection with the accompanying drawing wherein, v

Figure 1 illustrates an isometric dra'wing of'the physical structure of a preferred embodimentof my invention;

Figure 2 is a schematic circuit diagram of an ultra-high-frequency oscillator incorpor'ating my invention.

Referring now to the.drawing and more particularly to Figure 1,1rny invention is illustrated in a practical unitary a'ssembly comprisinga pair of variable capacitors l and 1 I, havinga'rotor 12, a stator l3, and 'arotor 1'4, astat'or '13, respectively. The plates of rotors l2 and "ll-are afiixed and ganged to a shaft [5, which is supported in bearings containedon square-end-plates l6 and- IT, made of insulation material su'ch'as polystyrene or a similar'substance having desirable dielectric properties at ultra high-fre quencies. One end of shaft l5 extends through the bearing on plate 16, thereby enabling rotation 'of the shaft by a knob or similarme'ans. A metallic spring wing interposed between rotor and end plate H maintains frictional contacttherebetween-and prevents slippage of the setting- 6f shaft [5. The stators l3 and Ii, which ire meshed with rotors l2 and are supported by connecting rods I8 and", the extremities there'- of being rigidly secured to their-respect'ire end plates l6 and l1.

The holes 2 l, bored throughindented portions of the end plates l6 and 11,-a're-for' the purpose of receiving machine screws for-"mounting the structure on a panel or chassis.

The connecting rods -|8"an'd IB and shaft-f5 function as a transmission line and their dimensions are governed by the desired=cperating frequency range of the unit. Electrical connection to the tuning unit is made throughsolderin'g 22 which is attached 'totherotor H- of condenser H and soldering lug which ls attacheddothe stator l5 of condenser H.

Referring now to-Figure 2,-the tuning' unit'is illustrated schematically 'as applied in =a sementional ultra-high-frequeney-osclllatorcircuitemploying a triode tube 24. The-inductivebranch of the tuning unit consists '0! the combination of transmission line iiicomprising connecting capacitor 1 0 whichserves "to varythe effective inductanceof thebranch. Capacitor H isshunted across the inductive branch and operates in parallel resonance therewith, the resonance frequency being a function of the effective inductance of the combination of capacitor I0 with line 25 and the capacitance offered by capacitor l I.

Since the condensers l0 and I I are mechanically ganged, the efiective inductance and capacitanc'e of the tank is simultaneously varied so that the overall frequency change is far greater than attainable by a variationlof a sim le cond'enser in a tank circuit. Moreover since the ef- "fective'inductance is varied in coordination with the variation in tank capacitance, the LC ratio 'i'snot substantially disturbed throughout the tun- It will be apparent that variou modifications and=changes may be made without departing from the spirit and scope of the invention provided "such modification and changes fall fairly within the spirit and scope of the claims hereinafter appended.

I claim:

1. The combination in a parallel-resonant circuit comprising an inductor having capacitive means for varying the eifective inductive reactance thereof, and a variable capacitor "mechanically ganged to said capacitive means and electrically shunted across said inductor whereby changes in thevalue' of said capacitor are accompaniedby changes inthe value of said inductor.

2. The combination in a parallel resonant circuit comprising atransmission line'of -a length adapted toact as an inductance within a prescribed frequency range, a first variable capacitor shunted across one end of said linefor varying the efiective length thereof, a second variable co.- pacitor shunted across the other end of said line in parallel resonance therewith, 'and'mechanical meansforiganging said first and second capaci- 4 tors 3. The combination'in :a parallelresonant circuit comprising a'flrst variable capacitor, .a'sec- 0nd variable capacitor colinearly disposed in respect torsaid capacitor, and a transmission line connecting-said :capacitors in paraflel, one conductor thereof mechanicallyganging said capacitors,

4.1n a resonant structure vthe combination comprising a pair of spaced end plates in parallel relation, each having a central bearing, a :pair of parallel rods connectingsaid end plates, ashatt extending between said'beanlngs, a'flrst variable condenser having its stator mounted across said rods at one end thereof-and itsrotor -mounted at one end of said shaft, and a second-condenser having its stator mounted across said rods atthe other end thereof and its rotor mounted at the other end of said shaft whereby saldfirst .and second condensers may be simultaneously varied,

said rods and saidshaft beingnrranged'as toto'rm a transmission .line of 'a length adapted to act an inductance within a.1prescribed :frequency range, whereby said line in combination with said first and second condensers form a parallel resonant circuit. A I

EDWlN P. THIAS. 

